Assessment of Safety for Anchor Handling Operation

Abstract

The objective of this paper is to evaluate the stability performance of an AHTS in operations. After the accident with the anchor handling vessel (AHTS) Bourbon Dolphin (which capsized in 2007), it was Clear that the existing criteria for the anchor handling vessel were no longer sufficient. There is an ongoing discussion that whether the criteria should be updated or not. The IMO criterion is the main criteria for special purpose vessel such as offshore supply vessel. But Bourbon Dolphin is a combined vessel with PSV and AHT. After that, NMD has suggested new criteria for the anchor handling vessel. The most important thing is to evaluate the heeling moment during the operation. Several aspects regarding to operation should be studied. Because of the characteristics of the operations, the criteria may vary among different loading conditions. NMD report has proposed some suggestion for people to determine the characteristics of mooring load. To describe the stability performance of an AHTS in operations, a computer program Maxsurf Stability is used to calculate the static stability curves and equilibrium data in various loading conditions. The vessel stability mainly depends on the propulsion system, mooring load, external forces such as current, wind force or dynamical load. In the paper, there are some researches of mooring load parameters such as the angle beta between mooring line and center line and the angle alpha between mooring line and vertical axis. The angle alpha can be ignored while calculating the mooring load due to its small effect. After application of criteria, the maximum permissible tension will be figured out. These analyses are carried out under the vessel’s working loading condition. In addition to this research, a sensitivity analysis based on modification of IMO weather criteria o can be studied. The results can be useful while designing work of anchor handling vessels and further work of analysis of AHTS.